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Discussion Starter #1
Recently my 89 Ford Bronco v8 5.0l tachometer has been bouncing randomly up and down dramatically without acceleration. From 2,000 to 6,000 and back down again without a change in the actual RPMs. I recently got a Code 34 which could be one of three things

1. EGR control circuit fault
2. EVAP control system fault/ voltage higher than closed limit
3. Defective EGR pressure transducer

I replaced both the EGR solenoid and EGR valve position sensor 13,000 miles ago. Recently while driving and the tachometer was going crazy, my truck had a hiccup and hit neutral a few times mid-drive without me changing position of the gas pedal. It’s a rough drop then continues to drive back to normal. My muffler got really hot within a short distance of driving. Do I need a whole new EGR? Lower intake tube? Due to carbon build up?

Also, symptoms of a bad EGR control solenoid is pinging or knocking. I’ve had this ping under slight gas and inbetween it swtchig gears that lasts a second and disappears once gears switch. With this new problem, the pinging isn’t as loud or doesn’t happen? Strange
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Welcome to FSB!

@miesk5 will be along shortly to help ya out. Idk nothing about codes
 

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Discussion Starter #3
Welcome to FSB!

@miesk5 will be along shortly to help ya out. Idk nothing about codes
Thank you. I replaced the EGR valve, EGR valve position sensor, EGR vacuum solenoid, and oxygen sensor. Also connected it to a different battery. Still had the same problems. Where is the tachometer connection under the hood? Thank you
 

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Yo 89EddieMelvin,
WELCOME!
Tachometer is fed directly from the coil negative.
Check for loose wiring connections at coil on driver side of engine or at instrument cluster connector .
Are connections loose?
Yes, SECURE loose connections.
No, Inspect instrument cluster printed circuit for damage, poor connections, or open circuits.
Is instrument cluster printed circuit open or damaged? If Yes, find a shop that repairs EECs, ABS Control Modules, etc.such as https://www.ebay.com/usr/modulemechanics which has a great review by a member here.


Screenshot_20191231-101806.jpg
Screenshot_20191231-101739.jpg

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Here are the 1989 EVTM, Emissions & Pre-Delivery Manuals, Partial via mrnewland1 in Google Drive @
https://drive.google.com/drive/mobile/folders/0Bz1eScc6s4raOHd0WlVnMUw4WjQ?usp=drive_web
Slow scrolling so download for the table of contents, etc.
Above fuse panel depiction and wiring diagram are from this EVTM.

1989 Bronco Dealer Brochure @ 1989 Ford Bronco

1989 Bronco Lubricant Specifications by Ford via Gary @ http://www.garysgaragemahal.com/lubricant-specifications.html

Free registration for some wiring diagrams (86 through 96) and Technical Service Bulletins, (80 through 96), same as by Ford @ BBB Industries- Premium Alternators, Starters, Power Steering Products | TSB's & Wiring Diagrams

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Al
 

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Yo,

DTC 34 - EGR voltage above closed limit
...in Key On Engine Off (KOEO) or Engine Running (KOER) Self-Tests; indicates that the EGR valve may not be fully seated in the closed position; or the EVP sensor voltage is greater than the closed limit voltage of 0.67 volt. Because of the preload on the installed EVP sensor, it is very difficult to determine whether the EGR valve is seated or the EVP sensor is in contact with the EGR valve stem.
•Faulty Vacuum system - See my Vacuum leak test in post #11 incl some jowens HVAC Control Panel pics/info @ https://www.fullsizebronco.com/forum/21-noobie-bronco-tech-questions-flame-free-zone/206824-help-dtc-codes-idle.html
One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.

•Damaged EVP sensor
•Corroded or dirty connector
•Damaged EGR valve
•Broken wire in harness
•Grounded harness
•Damaged Computer

- Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat.
Remove the EGR valve and clean it with carbon remover and a brush if necessary

Prior to re-installing see if you can blow air through the flange side of the EGR by mouth.

EGR Valve Position (EVP) Sensor Testing @ Ford Fuel Injection » EGR Valve Position sensor (EVP)
by Ryan M
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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Yo AL,

What would we do without you (y)
 
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Discussion Starter #7
Recently my tachometer has been bouncing without change in the motor or rpms itself. I got a code 34 and replaced EGR valve, EGR valve position sensor, EGR vacuum solenoid, oxygen sensor, battery and battery terminals. I had a few hiccups while driving, like fuel pump surge, and had it die on me a couple times when letting off the gas. Now it struggles to start sometimes and wants to die. Checked vacuum lines with starting fluid. Checked fuel pressure 35 psi at an idle. You hear the low pressure fuel pump in the tank when key is turned. Checked the pcv valve and replaced the line and valve itself. Got a couple random codes (67, 15) after a couple test drives then they disappeared. Then code 34 is back. Gas cap is good. Cleaned inside lower intake tube of EGR. Recently changed oil, oil filter, air filter, added a bottle of LUCAS transmission fix cause I had a leak and the fluid level is good while idling in park. Replaced ignition control module about 13k miles. Could that be problem? I am so lost. Here are some other things I’ve recently done. I replaced tps 13k miles ago, ignition coil and wire 4K miles ago, new ignition coil connection wires, new spark plugs (gapped at 40 rather than 44 to stop pinging) and wires 13k miles ago, sea foamed the engine at the same time, new distributor cap 17 k miles ago, new thermostat, new water pump and hoses, just replaced transfer case with used one off different bronco, new ignition control module 6k miles ago, new EEC relay, new low pressure fuel pump, fuel filter, checked knock sensor, fixed a few holes in random lines, cleaned up some crimped wires.

Someone please help me get to the bottom of this!
 

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Check grounds. Ensure your battery cables are good and take a good look at the connections. There are several grounding points, inspect them all- I don't have a diagram for your year, but a quick Google will show you where they are.
 

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Agree on checking grounds. And the battery cable replacement. My 96 did odd things. Such as cranking longer to start or odd mis fire. Replaced the battery cables with much larger ones, and it ran a lot better and the odd things disappeared.
 

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I've had a bouncing tach twice in my 28 years of driving Broncos.

1st time was coil wire. Tach started bouncing/ fluttering at one point. About a mile down road then engine started running rough and started bouncing more. Turned around and headed home. Truck died just before my driveway and I coasted into the driveway. Popped the hood and the coil wire BURNT IN HALF at the connection to the distributor cap. Wires were only a year old and were Motorcraft.

2 time. I have video of the bouncing which I'll include. My current Bronco, guy said it had a miss when i bought it and he couldn't figure it out.


Number 5 & 6 wires were right next to each other in the wire loom. Ford has issued a TSB regarding wires 1 & 3, and 5 & 6 and how to route the wires so that you don't get crossfire. Rerouted the wires and it went away.


Regardless, if you're having a bouncing tach, it's usually a result of electrical current that can't ground itself and finds its way back to the tachometer. The coil wire transfers spark more times than spark plug wires themselves as it feeds the distributor. I'd start there even if your wires are only 13k miles old. Both times I've experienced this, had to do with spark plug wires.
 

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Yo @89EddieMelvin

I merged your two threads here.
Single-Function Reservoir Testing in 88-89; "...Used on '88-89 Broncos & F-series/E-series/Rangers/others with single tank dual-pump EFI.
152170


In this version, the only moving part is the tank-side inlet check valve. The return ports flow freely and are NOT connected to the reservoir. The engine-side supply port is open to the reservoir. To test it, unplug the frame fuel pump, disconnect the engine-side supply (large) line, and cycle the key. If fuel flows out of the reservoir nipple, the reservoir is working normally. If not, disconnect the tank-side supply (large) line, and cycle the key. If fuel flows out of the line, the reservoir check valve is probably stuck, or its internal filter is clogged.

A reservoir marked "DO NOT REMOVE CUP" does not contain a filter. For a replacement O-ring for the cup, buy a NAPA 3268 (or equivalent) filter...
..."The Ford engineering number on the filter is E6TZ-9365-A...." by Steve

As advised;
Check both battery posts, cables, connectors & GROUNDS for looseness and corrosion. If you see corrosion on a cables' wires strands between connectors or lugs and leading into the insulation, peel back the insulation to see how far back it reaches.
by by El Kabong
"Cheesy clamp on end. Do not use for a long term repair. Only to get you home when nothing else is available. If you have one of these, suspect it before anything else" by El Kabong @ Common Replies to FAQs

Check starter relay for looseness or rust to the inner fender. It's ground is through its body to the inner fender.
Check that starter is mounted securely and connectors are clean and tight.

Engine Block pic in a 94 5.8; "...The black battery wire goes from the front bolt of the engine mount (on the block) to this tab & up to the battery post, where a smaller black wire goes to the core support, providing a continuous ground path between the engine, frame, battery, & body..." could be close to same for your 89

Source: by CodysBigBlueBronco (how much $???)

Intake Manifold to Block Strap Location pic in a 96 5.0
Source: by boss (bossind, Steve) at SuperMotors.net

it is between 2nd & 3rd plugs on passenger side
Could be same for 89
..
You can find locations of other grounds in the 1989 Ford EVTM, EmissionsManual I posted in my first reply above,.


Spark Plug Wire; Routing @ 1992 Ford Bronco wires pictures, videos, and sounds | SuperMotors.net by Tank92

The firing order for 1987-1993 5.0Ls is 1-5-4-2-6-3-7-8. If #7 and #8, or #2 and #4 spark plug wires are routed next to each other at the separation bracket, an induction crossfire condition can occur.
 

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Discussion Starter #12
I will definitely check that again. But my tachometer bouncing is way more dramatic. It can change from 2-5000 rpms in a second and back down again. Seems electrical. I replaced the plastic connector piece that has two wires coming out of it that plugs into the ignition coil, could the new one be faulty? Ordered a cheap one
I've had a bouncing tach twice in my 28 years of driving Broncos.

1st time was coil wire. Tach started bouncing/ fluttering at one point. About a mile down road then engine started running rough and started bouncing more. Turned around and headed home. Truck died just before my driveway and I coasted into the driveway. Popped the hood and the coil wire BURNT IN HALF at the connection to the distributor cap. Wires were only a year old and were Motorcraft.

2 time. I have video of the bouncing which I'll include. My current Bronco, guy said it had a miss when i bought it and he couldn't figure it out.


Number 5 & 6 wires were right next to each other in the wire loom. Ford has issued a TSB regarding wires 1 & 3, and 5 & 6 and how to route the wires so that you don't get crossfire. Rerouted the wires and it went away.


Regardless, if you're having a bouncing tach, it's usually a result of electrical current that can't ground itself and finds its way back to the tachometer. The coil wire transfers spark more times than spark plug wires themselves as it feeds the distributor. I'd start there even if your wires are only 13k miles old. Both times I've experienced this, had to do with spark plug wires.
[/QUOTE

online
 

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I will definitely check that again. But my tachometer bouncing is way more dramatic. It can change from 2-5000 rpms in a second and back down again. Seems electrical. I replaced the plastic connector piece that has two wires coming out of it that plugs into the ignition coil, could the new one be faulty? Ordered a cheap one
The video I posted was the second time it happened. The first time when the coil wire burnt in half, it started like the video then it was going REALLY HAYWIRE up until the truck died.
 

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Discussion Starter #14
Could all my problems be caused by a faulty DPFE sensor? I did more research on Code 34 and found that sensor is part of it. Failing sensor can cause chugging like I’ve been having. Where is this sensor located?
Yo @89EddieMelvin

I merged your two threads here.
Single-Function Reservoir Testing in 88-89; "...Used on '88-89 Broncos & F-series/E-series/Rangers/others with single tank dual-pump EFI.
View attachment 152170

In this version, the only moving part is the tank-side inlet check valve. The return ports flow freely and are NOT connected to the reservoir. The engine-side supply port is open to the reservoir. To test it, unplug the frame fuel pump, disconnect the engine-side supply (large) line, and cycle the key. If fuel flows out of the reservoir nipple, the reservoir is working normally. If not, disconnect the tank-side supply (large) line, and cycle the key. If fuel flows out of the line, the reservoir check valve is probably stuck, or its internal filter is clogged.

A reservoir marked "DO NOT REMOVE CUP" does not contain a filter. For a replacement O-ring for the cup, buy a NAPA 3268 (or equivalent) filter...
..."The Ford engineering number on the filter is E6TZ-9365-A...." by Steve

As advised;
Check both battery posts, cables, connectors & GROUNDS for looseness and corrosion. If you see corrosion on a cables' wires strands between connectors or lugs and leading into the insulation, peel back the insulation to see how far back it reaches.
by by El Kabong
"Cheesy clamp on end. Do not use for a long term repair. Only to get you home when nothing else is available. If you have one of these, suspect it before anything else" by El Kabong @ Common Replies to FAQs

Check starter relay for looseness or rust to the inner fender. It's ground is through its body to the inner fender.
Check that starter is mounted securely and connectors are clean and tight.

Engine Block pic in a 94 5.8; "...The black battery wire goes from the front bolt of the engine mount (on the block) to this tab & up to the battery post, where a smaller black wire goes to the core support, providing a continuous ground path between the engine, frame, battery, & body..." could be close to same for your 89

Source: by CodysBigBlueBronco (how much $???)

Intake Manifold to Block Strap Location pic in a 96 5.0
Source: by boss (bossind, Steve) at SuperMotors.net

it is between 2nd & 3rd plugs on passenger side
Could be same for 89
..
You can find locations of other grounds in the 1989 Ford EVTM, EmissionsManual I posted in my first reply above,.


Spark Plug Wire; Routing @ 1992 Ford Bronco wires pictures, videos, and sounds | SuperMotors.net by Tank92

The firing order for 1987-1993 5.0Ls is 1-5-4-2-6-3-7-8. If #7 and #8, or #2 and #4 spark plug wires are routed next to each other at the separation bracket, an induction crossfire condition can occur.
152308
 

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Discussion Starter #15
Does anyone have a diagram to show where the DPFE sensor is on 89 Bronco v8 5.0 ?
 

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Discussion Starter #17
Oh shoot. Ok thank you
there is no DPFE sensor. only the 96 had them.
you have a EVP sensor which si the sensor on top of the EGR valve
 

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Could all my problems be caused by a faulty DPFE sensor? I did more research on Code 34 and found that sensor is part of it. Failing sensor can cause chugging like I’ve been having. Where is this sensor located?
Yo Eddie,
Only 95 5.8L California emission models & all 96 have the Differential Pressure Feedback (DPFE) Sensor instead of EGR Valve Position (EVP) Sensor.

That code source included other Ford models as well as our Broncos.
For a Bronco specific Code list see Ford Fuel Injection » 2 Digit Self-test Codes 11-32
by Ryan M
Iggie PFE in Code 34 & 35
See Ryans collection of other info.
 
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